1. Field of the Invention
The present invention relates to a method and apparatus for controlling the transmission frequency in a serial advanced technology attachment (SATA). More particularly, the invention is related to a method and a related semiconductor apparatus for minimizing communication errors potentially occurring when a standard transmission frequency changes due to temperature variations and/or jitter by appropriately controlling the transmission frequency used between a host device and SATA device.
This application claims the priority of Korean Patent Application No. 10-2006-0032172, filed on Apr. 10, 2006, the subject matter of which is hereby incorporated by reference.
2. Description of the Related Art
SATA is a next-generation data transmission method providing about twice the operating speed of conventional parallel advanced technology attachment (PATA). SATA technology is characterized in one aspect by the use of a simple external connection cable that facilitates electrical connection and mechanical assembly. A first generation SATA (1.0) specification is complete. It is also expected that second generation SATA and third generation SATA related to entry-level servers will soon be completed.
The interface structure associated with SATA includes a data cable, a power cable, and a connector. FIG. 1 illustrates a conventional SATA interface 10. Referring to FIG. 1, interface 10 includes twin data cables 100, five power cables 110, host connectors 120 and 130, and associated device connectors 140 and 150.
While PATA uses a power supply voltage swing of five volts (5.0 V), SATA uses a power supply voltage swing of only one-half a volt (0.5 V). Accordingly, during data transmission, electromagnetic effects and related data signal interference is reduced and power consumption is markedly decreased. However, when the power supply voltage swing is thus reduced, the possibility of signal distortion due to external interference increases. To overcome this potential problem, SATA uses a differential data transmission scheme.
The twin data cables are used in SATA to accomplish differential data transmission. Each data cable essentially forms a separate data path. In each data path, data is transmitted in only one direction. For example, data is always transmitted from a SATA compliant host controller to an attached device comprising a SATA compliant controller using one of the two data paths, while data is always transmitted from the attached device to the host controller using the other data path. Accordingly, timing skew potentially caused by a time difference between these separate data transmissions does not occur and data may be transmitted at relatively higher frequencies. For example, first generation SATA provides for an operating frequency of 1.5 GHz (i.e., a data transmission rate of 150 Mega bits per second).
Generally, the data communications enabled by a SATA interface occur at a specified standard transmission frequency. Both the host and the attached device generate the specified transmission frequency using respective crystal oscillators.
The crystal oscillators required to generate the standard transmission frequency are very sensitive to temperature. When the temperature of the host or attached device changes during operation, the standard transmission frequency defined by the output of the crystal oscillator may also change. Any change in the standard transmission frequency may cause a data communication error.
Generally, the host and attached device have a receiver frequency offset range adapted to unilaterally compensate for some moderate drift in the standard transmission frequency. Within this receiver frequency offset range, a change in the standard transmission frequency will not result in a data communication error. However, this capability presupposes a stable standard transmission frequency within each device and this may not be the case. For example, if a changed transmission frequency transmitted from the host and received by the attached device is within the receiver frequency offset range, a returning standard transmission frequency is typically transmitted back to the host by the attached device without a data communication error. However, since the standard transmission frequency may have changed again (or further) in the host during the first transmission period, the returning transmission may be interrupted as containing errors.
FIG. 2 is a flowchart of a communications method adapted for use with a conventional SATA interface. In operation S210, a transmission frequency is detected from a signal received from a host or an attached device. In operation S220, it is determined whether the detected transmission frequency is within a receiver frequency offset range. If the detected transmission frequency is not within the receiver frequency offset range, a communication error is determined in operation S240. Accordingly, an associated controller performs one or more transactions corresponding to the detected communication error. However, if the detected transmission frequency is within the receiver frequency offset range, data is transmitted between the host and the attached device at a specified standard transmission frequency in operation S230.
FIG. 3 is a conceptual diagram illustrating the generation of a communication error occurring during a conventional exchange of data. In the illustrated example of FIG. 3, the standard transmission frequency generated by a crystal oscillator in a host using second generation SATA technology is assumed to change in response to temperature variations.
For example, it is assumed that a standard transmission frequency of the host migrates to 1.6 GHz due to a change in the ambient operating temperature from a specified standard transmission frequency of 1.5 GHz. As a result, a receiver frequency offset range within the host is defined between 1.55 through 1.65 GHz. Hence, the host transmits data to the attached device at the changed transmission frequency of 1.6 GHz. The attached device receives the transmitted data, detects a transmission frequency of 1.6 GHz, and determines whether the detected transmission frequency is within the receiver's frequency offset range of 1.45 GHz to 1.65 GHz. Since the detected transmission frequency of 1.6 GHz is within the receiver frequency offset range of the attached device, it then normally return transmits data to the host at the standard transmission frequency of 1.5 GHz.
However, the receiver frequency offset range of the host has been defined in a range of between 1.55 GHz to 1.65 GHz in due to a change in the ambient operating temperature, or some other factor. Accordingly, when the return data signal from the attached device is received at the host at the correct (e.g., as specified) standard transmission frequency of 1.5 GHz, the previously established host receiver frequency offset range of 1.55 GHz to 1.65 GHz results in the generation of a communication error.
Thus, it is clear that an improved method of data communications is required that reduces communication errors occurring due to changes in a standard transmission frequency.